1. Field of the Invention
The subject invention relates to a system and method for determining a voltage in each cell of a plurality of battery cells connected in series and verifying the accuracy of the determined voltage.
2. Description of the Related Art
Electric vehicles and hybrid-electric vehicles typically utilize numerous cells (i.e., batteries) for powering electric drive motors and other electric equipment. These cells are often connected together in a series relationship, as is well known to those skilled in the art, to provide higher voltages.
Due to variations between individual cells, such series-connected cells require periodic balancing, i.e., charge equalization, to maintain a steady voltage and prevent premature failure. One difficulty in cell balancing is determining which cell or cells may need to individually charged or replaced. Therefore, it is necessary to provide a system to determine the voltage in each cell.
Numerous systems and techniques have been developed to address this necessity. Prior art systems often utilize one or more capacitors between the cells and the amplifier such that a more stable and accurate voltage may be measured. For instance, U.S. Pat. No. 6,362,627 (the '627 patent) to Shimamoto et al. discloses a system with a plurality of cell switches connected to various cells, a capacitor connected to the cell switches, and an amplifier connected to the capacitor. Japanese Patent Abstract Publication No. 2003240806 (the '806 publication) to Yazaki Corporation discloses a system for measuring voltage of individual cells in a plurality of cells connected in series. The system includes a plurality of cell switches electrically connected to the plurality of cells with one switch connected on each side of each cell.
Unfortunately, cell measurements using capacitor-based prior art systems such as these may not always be accurate due to circuit malfunctions, faults, and device degradation. Said another way, although these problems may be occurring, they may not be reflected in the cell voltage measurement via the capacitor. Therefore, there remains an opportunity for a system and method for measuring voltage of individual cells connected in series having improved accuracy.